Help! on Tire sizes 1971 C10

[mdeal]

Ok guys, I know there are a lot of posts about this topic. I'm still finding it hard to make my decision on what tire size to go with.
I have a 1971 C10 2wd, lowered using CPP's 5" spring kit.
I have purchased Boss 338 (I know they're overdone...but I'm on a budget)
18X8 in the front and 18X9.5 for the rear.

I've been thinking about 245/45R18 for the front and 275/40R18 for the rear...
I just don't want to buy these sizes and install them and have so much fender gap I could check my brakes by sliding my head in between the fenderwell and the tire! I want to fill the fenderwell and not have them look like balloons either. I'd like the sidewall to be pretty straight(slight bow outward is ok).

Please!!! Any suggestions would be great! Pictures would be even better!!

Thanks again!